1. Field of Invention
This invention relates to sensing fluid quantity in a refillable fluid container.
2. Description of Related Art
Fluid ejector systems, such as drop-on-demand liquid ink printers, have at least one fluid ejector from which droplets of fluid are ejected towards a receiving sheet. Scanning ink jet printers are equipped with fluid ejection heads containing fluid ink. The ink is applied to a sheet in an arrangement based on print data received from a computer, scanner or similar device. To control the delivery of the fluid to the sheet, fluid ejection heads are moved across the sheet to provide the fluid to the sheet, which is ejected as drops. These drops correspond to a liquid volume designated as pixels. Each pixel is related to a quantity needed to darken or cover a particular unit area.
In order to lower cost and improve performance by limiting inertia, moving-head fluid ejection systems are designed with low weight fluid ejection heads that often use refillable fluid containers. In order to minimize weight, the fluid ejection heads contain a relatively small quantity of fluid. Consequently, the fluid ejection heads (or their fluid reservoirs) must either be replaced or refilled periodically. Replaceable cartridges are commonly used in home-use printers. Some heavier-use printers in industry attach the fluid ejection head via an umbilical tube to a larger tank for continuous refilling. Other heavier-use printers refill the fluid ejection head periodically.